Super high quality laser-ultrasound signals for aircraft component inspection

Abstract
Laser-ultrasound has demonstrated important cost saving for the inspection of aircraft components in the past few years. Unfortunately, in some specific challenging cases, sensitivity is not sufficient and averaging appears as the obvious means to bring signal-to-noise ratio (SNR) to acceptable levels. To avoid averaging, and in the cases where background noise is not a limitation, SNR can be significantly increased by rejecting amplitude and phase laser noise, by reducing generation pulse duration, and by adapting optical wavelength of the generation laser to the desired optical penetration depth. In this paper, we present techniques to produce large SNR signals by rejecting laser noise and by generating ultrasonic waves using new laser sources. Laboratory experimental results obtained with those techniques and experimental improvements resulting from the implementation of a shorter pulse laser in an industrial setup are reviewed.